Hippo signaling is an emerging tumor suppressor pathway that plays key roles in organ size control and tumorigenesis. Hippo signaling inhibits the transcription co-activator Yes-Associated Protein (YAP), an oncogene amplified in multiple cancers, including hepatocellular carcinoma, colon and ovarian cancer. YAP promotes cell proliferation, epithelial-to-mesenchymal transition (EMT), survival and chemoresistance. Therefore, it is important to understand how YAP activity is regulated for the development of novel cancer therapeutics. We recently discovered that cellular energy level is a novel upstream signal regulating Hippo pathway, through the central metabolic sensors LKB1 and AMP-activated protein kinase (AMPK). Consistently, small molecule activators of AMPK inhibit YAP activity; and YAP is activated in LKB1-deficient cancers. Further understanding this novel signaling mechanism will shed light on how cellular metabolism regulates YAP oncogene. Our specific aims of this proposal include: (1) To determine the mechanism(s) of metabolic regulation of tight junctions and Hippo signaling. (2) To investigate the roles of tight junction proteins as the central signaling node in regulation of YAP; and to investigate YAP as a downstream oncogenic factor in LKB1-deficient lung cancer. (3) To determine whether activation of AMPK inhibits YAP in vivo; and to target LKB1-deficient lung cancer cells in vitro and in vivo using small molecule inhibitor of YAP-TEAD interaction.